In a workpiece cleaning apparatus used in the prior art TFT-LCD (Liquid Crystal Flat Panel Display) industry, a detection device is required to detect positional information of a workpiece during conveying and cleaning of the workpiece and to send a detection signal to the control system of the apparatus.
The existing detection device generally employs an optical fiber sensor or a proximity switch. The optical fiber sensor includes an emitter and a receiver, and the emitter and the receiver are both mounted above the conveyor section of the workpiece cleaning apparatus. In use, when a workpiece is conveyed to the conveyor section, light emitted from the emitter is reflected by the workpiece, and the reflected light is received by the receiver, thereby the position of the workpiece is measured. The controller of the apparatus can control the switch to be on or off based on a signal. However, it is further required to spray liquid to clean the workpiece when the workpiece is conveyed in the conveyor section, and light would be refracted and reflected by the liquid. Therefore, when light is refracted, there exist detection errors; when light is reflected, the light emitted from the emitter may be reflected into the receiver, resulting in false control. Consequently, there is a risk of occurrence of workpiece collision. The proximity switch achieves the purpose of controlling the switch to be on or off by making use of the displacement sensor's characteristic of being sensitive to a proximal object. The proximity switch is excellent in stability but poor in water resistance, thus it cannot be used in a liquid environment.
Meanwhile, in the TFT-LCD industry, high-pressure deionized water (De-Ion water) is generally used for washing. Since the pressure of the high-pressure deionized water is detected using the water inlet pressure in the pipeline, the water outlet pressure and abnormalities in use (including the problems such as excessive water pressure resulting from nozzle falling-off, pipe crack, abnormal spraying direction, and so on) cannot be detected accurately and effectively, so that abnormalities including abnormal cleaning, remaining water stains upon drying, and the like would consequently occur.